Method of gas separation and membranes therefor

Abstract

An improved method of gas separation and novel polyimide membranes are disclosed and claimed. Membranes in accordance with the present invention include the condensation product of fluorinated diamines such as 2,2'-bis(3-aminophenyl)hexafluoropropane, 2,2'-bis(4-aminophenyl)hexafluoropropane and 2-(3-aminophenyl)-2'-(4-aminophenyl)hexafluoropropane with aromatic dianhydrides such as 3,3', 4,4' benzophenone tetracarboxylic acid dianhydride.

We claim: 
     
       1. In a process for separating gasses comprising bringing two or more gasses under pressure into contact with one side of a molecularly permeable membrane formed of an aromatic polyimide such that a portion of said gasses is forced through said membrane, the improvement comprising utilizing a polymeric membranous structure having recurring units of the chemical formula ##STR13## where: m is an integer from about 15 to about 250 R is a tetravalent aromatic radical selected from the group consisting of: ##STR14## or mixtures thereof; ##STR15## or mixtures thereof;   
     
     
       Ar' is ##STR16## or mixtures thereof; X 1 , . . . X 8  being defined hereinbelow ##STR17## or mixtures thereof 
     
     
       Ar' is ##STR18## or mixtures thereof; R', Z being defined as hereinabove; X 1 . . . X 8  are independently H, alkyl groups with 1-6 carbon atoms; Br, Cl; or aromatic groups with 6-13 carbons where Ar and Ar' are nonidentical where Ar and Ar' are nonidentical. 
     
     
       2. The process according to claim 1, wherein said membrane exhibits a permeability of at least about 15 Barrers with respect to helium. 
     
     
       3. The process according to claim 2, wherein said membrane exhibits a permeability of at least about 0.4 Barrers with respect to oxygen. 
     
     
       4. The process according to claim 3, wherein said membrane exhibits a permeability of at least about 0.05 Barrers with respect to nitrogen. 
     
     
       5. The process according to claim 1, wherein said membrane exhibits an ideal separation factor of at least about 85 with respect to a helium/methane mixture. 
     
     
       6. The process according to claim 1, wherein said membrane exhibits an ideal separation factor of at least about 35 with respect to a carbon dioxide/methane mixture. 
     
     
       7. The process according to claim 1, wherein said membrane exhibits an ideal separation factor of at least about 2 with respect to a nitrogen/methane mixture. 
     
     
       8. The process according to claim 1, wherein said membrane exhibits an ideal separation factor of at least about 5 with respect to an oxygen/nitrogen mixture. 
     
     
       9. A polymeric membranous structure for gas separation having recurring units of the chemical formula; ##STR19## where: m is an integer from about 15 to about 250 R is a tetravalent aromatic radical selected from the group consisting of ##STR20## or mixture thereof; Z is a divalent radical selected from: ##STR21## or mixtures thereof; Ar is ##STR22## or mixtures thereof; X 1 . . . X 8  being defined hereinbelow ##STR23## or mixtures thereof; Ai is ##STR24## or mixtures thereof; R', Z being defined as hereinabove;   X 1  . . . X 8  are independently H, alkyl groups with 1-6 carbon atoms; Br, Cl; or aromatic groups with 6-13 carbons where Ar and Ar' are nonidentical.   
     
     
       10. The membrane according to claim 0, wherein said membrane exhibits a permeability of at least about 15 Barrers with respect to helium 
     
     
       11. The membrane according to claim 10, wherein said membrane exhibits a permeability of at least about 0.4 Barrers with respect to oxygen. 
     
     
       12. The membrane according to claim 11, wherein said membrane exhibits a permeability of at least about 0.05 Barrers with respect to nitrogen. 
     
     
       13. The membrane according to claim 9, wherein said membrane exhibits an ideal separation factor of at least about 85 with respect to a helium/methane mixture. 
     
     
       14. The membrane according to claim 9, wherein said membrane exhibits an ideal separation factor of at least about 35 with respect to a carbon dioxide/methane mixture. 
     
     
       15. The membrane according to claim 9, wherein said membrane exhibits an ideal separation factor of at least about 2 with respect to a nitrogen/methane mixture. 
     
     
       16. The membrane according to claim 9, wherein said membrane exhibits an ideal separation factor of at least about 5 with respect to an oxygen/nitrogen mixture. 
     
     
       17. A membrane for gas separation consisting of a polymeric condensation product of a diamine selected from the group consisting of 2,2,-bis(3-aminophenyl)hexafluoropropane, 2,2'-bis(4-aminophenyl)hexafluoropropane and 2-(3-aminophenyl)-2'-(4-aminophenyl)hexafluoropropane or mixtures thereof and a - dianhydride selected from the group consisting of 3,3', 4,4'benzophenone tetracarboxylic acid dianhydride, 2,2-bis(3,4 dicarboxyphenyl)hexafluoropropane dianhydride, 3,33',4,4'diphenyl tetracarboxylic acid dianhydride and mixtures thereof 
     
     
       18. The membrane according to claim 17, wherein said polymeric condensation product has a molecular weight, M w  of at least about 100,000.